Mk5 Auto Inflator by United Moulders

The United Moulders Mk5 Auto Inflator is probably the most widely used auto inflator used in lifejackets in the UK.

UML Mk5 Info


The Yellow Inflator is the newer version post 2009 and uses a 13mm clip.

The Black Inflator as seen on the image above right, is the older version that uses a 17mm clip.

Both Black and Yellow inflators work in the same way and so the information below applies to both.

You can find the link to the rearming kit or the individual parts used in the United Moulders Mk5 Auto Inflator here.

When you buy the rearming kit, RTS includes an information sheet which will help you rearm your lifejacket and give you some additional advise which you may find useful. But below are a few key points for you to consider.

DO NOT TRY TO SCREW THE CO2 CYLINDER IN FIRST!!! The firing pin may still be raised and the Cylinder will fire in your hand and could be very uncomfortable.

The first thing you have to consider with this device is the Mk5i Auto Cartridge.

Mk5 Auto Inflator

The Mk5 Inflator uses the UMA5000 model of the Auto Cartridge which has a green end cap. If the green cap is missing, it reveals the red underneath which is a warning. The Cartridge has a replace by date. RTS Rearming kits will have a good life span in excess of 3 years for the Mk5i Cartridge but 2 years is the maximum life span of the cartridge once fitted. The additional time allows for spares to be kept in appropriate storage conditions. More information is on the product page.

You should consider changing the auto cartridge before it reaches its replace by date. Some heavy users in the commercial sector change annually.

Screw the cartridge on to the Op Head until tight.

Mk5 Auto InflatorNext fit the side retaining clip. Make sure the lever is pushed back in to the Op Head before fixing the clip.

The Clip is part indicator, in that if you see the clip in place, green means good. If the clip is missing, you only see red which means warning, the device needs checking and assessing.

The Clip also serves a practical purpose. The clip provides some resistance so a proper tug is required to inflate your jacket, reducing the occurrence of accidental inflations caused by the manual toggle catching on something, or the lever working lose and raising the firing pin.

Next step is to check your Gas Seal Washer.

The gas seal washer should be sitting centrally inside the inflator Op Head. When you pull the toggle, the firing pin comes up through the hole in the middle of the washer and pierces the CO2 cylinder.

The washer has a dual function. It prevents CO2 escaping through the threaded area. It also creates a reverse pressure against the thread, meaning that the cylinder is less likely to work lose in wear.

Your RTS MK5 Auto Inflator rearming kit comes with a gas seal washer, which you only need to use if the current one is worn or missing.

Finally you can screw in your CO2 Cylinder.

Mk5 Auto Inflator

The Cylinder should be screwed in fairly tight.

CO2 Cylinders are engraved with a manufacture date but do not have an expiry date.

CO2 Cylinders only need to be replaced if the gas has been used or escaped, or if there are signs of damage such as rust.

Similarly the clip can last for a long time and only needs replacing if worn, broken or missing.

It is always handy to have a spare clip, auto cartridge and cylinder though, so that in the event of an inflation, the jacket can be put back in service quickly.

Link to United Moulders Technical Information.